Interbody fusion implant and related methods

ABSTRACT

An implant for performing interbody fusion within a human spine, inserters for such an implant, and associated methodology. The implant is preferably formed in situ from at least two separate but lockable members (a base member and a closure member). The base member may be implanted into an interbody space first, after which the end plates may be finally prepared and the base member packed with fusion promoting substances before engaging and locking the closure member. The closure member provides structural support for the adjacent vertebral bodies (along with the base member) and may be selected after implantation of the base member having a specific length, width, height, taper, etc . . . to ensure an optimal sizing of the implant for desired restoration of disc height, coronal taper, sagittal taper, etc . . .

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 12/834,855, filed Jul. 12, 2010, which claims benefit of U.S.Provisional Application No. 61/224,887, filed Jul. 12, 2009, thecontents of which are incorporated in full herein by reference.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to an implant for performing interbodyfusion within a human spine, inserters for such an implant, andassociated methodology. More specifically, the implant aspect of thepresent invention involves an implant formed in situ from at least twoseparate but lockable members (a base member and a closure member),wherein: (a) the base member may be implanted into an interbody spacefirst, after which the end plates may be finally prepared and the basemember packed with fusion promoting substances before engaging andlocking the closure member; and (b) the closure member providesstructural support for the adjacent vertebral bodies (along with thebase member) and may be selected after implantation of the base memberhaving a specific length, width, height, taper, etc . . . to ensure anoptimal sizing of the implant for desired restoration of disc height,coronal taper, sagittal taper, etc . . .

2. Discussion of the Prior Art

The human spinal column is made up of a series of vertebral bodies withintervertebral discs disposed there between, which collectively providesupport and structure for the body while allowing motion andflexibility, as well as protection for the spinal cord running throughthe spinal column and associated nerve roots which exit the spinalcolumn. Various traumatic events and/or degenerative conditions mayresult in undesirable motion or change in disc height, both of which maycause chronic pain for the affected individual. The degree and treatmentof pain varies by the individual but in many instances the pain can bedisabling and uncontrollable by conservative means, leaving surgery asthe only viable option. In many cases, the primary surgical treatmentinvolves interbody fusion, wherein an implant is introduced into thedisc space to restore the disc height and establish a bony bridgebetween the adjacent vertebral bodies with the goal of eliminating or atleast reducing the pain of the affected individual.

To enable the introduction of an interbody fusion implant, the surgeonmust perform the following steps to create a suitable environment forpost-operative fusion: (a) surgical access to the affected disc space;(b) an annulotomy to gain access into the interior of the affected disc;(c) an initial or preliminary discectomy to remove some or all of thenucleus pulposus within the affected disc; and (d) final endplatepreparation to remove the cartilaginous disc material to expose theunderlying bony endplates of the adjacent vertebral bodies (preferablywithout violating the bony endplates). Final endplate preparation is acritical step in implant placement and achieving a solid fusion. It isrequired to remove all the cartilaginous disc material while notviolating the bony end plate. Not removing the cartilaginous end platecan result in a delayed bony growth or incomplete bony growth, whilefracturing the bony end plate can result in a fracture of the vertebralbody and post-operative settling of the implant with concomitant loss ofdisc height and/or vertebral body alignment. Repetitive insertion ofinstruments into the disc space during the process of final endplatepreparation can result in possible injury to the neural and vascularstructures surrounding the disc space if the instruments areinadvertently passed or extended outside the disc space by the surgeon.

To help facilitate fusion, the implants preferably include one or more“fusion windows,” that is, apertures extending from the superior surfaceto the inferior surface of the implant to allow bone to form through theimplant to ensure a solid and robust fusion. To further facilitatefusion, these apertures may be filled with fusion promoting materialsincluding but not limited to cancellous autograft bone, allograft bone,demineralized bone matrix (DBM), porous synthetic bone graft substitute,bone morphogenic protein (BMP), mesenchymal stem cells and/orcombinations thereof and/or functional equivalents. Such materials aretraditionally introduced into the implant before the implant isintroduction into the disc space. Based on the oftentimes high amount offorce required to be applied to the corresponding insertion tools, suchfusion promoting substances can become loosened or dislodged during theintroduction of the implant, which can in certain instances increase theamount of time required to achieve fusion.

Implants can be introduced into the interbody space in one of severalknown approaches or directions to the spine, including posterior (fromthe back), anterior (from the front), and lateral (from the side).Before 2003, interbody fusion via a lateral approach was uncommonbecause of the inability to safely pass through the psoas muscle, whichflanks either side of the lumbar spine and includes the lumbar plexus.Lateral access surgery became safe and reproducible with the advent ofthe NeuroVision® system by NuVasive, Inc., which automatically detectsthe presence of nerves in the psoas muscle via surgeon-directedneurophysiology in combination with minimally disruptive accessinstrumentation (e.g. dilators, retractor, etc . . . ) to aid thesurgeon in avoiding nerves while establishing an operative corridor froma lateral approach.

The present invention addresses the need for additional interbodyimplant options, inserters, and techniques for use in lateral accesssurgery.

SUMMARY OF THE INVENTION

The present invention involves a novel interbody fusion implant for usein lateral access surgery, inserters for said implant, and associatedmethodology. The interbody fusion implant has two separate but lockablemembers (a base member and a closure member). According to an aspect ofthe present invention, the base member and closure member arecomplimentary to each other so that they can be engaged and thereafterlocked together while in a lumbar or thoracic interbody space. The basemember is configured in a generally elongated U-shaped manner withgenerally parallel side walls coupled to an end wall positionedgenerally perpendicularly with the side walls. The base member andclosure member may be equipped with any number of suitable lockingfeatures to lock the closure member to the base member.

According to an aspect of the present invention, the base member isintroduced into the interbody space before the closure member. By doingso, and given the U-shaped configuration of the base member, this allowsfor an aggressive final end plate preparation, inspection of the finalposition of base member within the disc space, and packing of fusionpromoting material after the base member is implanted but before theclosure member is implanted. This presents a host of benefits, whichwill be described in detail below, along with the specific method stepsassociated with the use of the base member and closure member duringlateral access surgery according to an aspect of the present invention.The introduction of the base member is facilitated through the use of aspecialized inserter designed to bolster the structural integrity of thebase member during insertion to reduce the likelihood of having the basemember fracture under the impaction forces typically involved ininterbody fusion procedures. The introduction of the base member is alsofacilitated via the tapered leading end, which serves as a general wedgebetween the adjacent vertebral bodies during insertion of the basemember into the disc space during impaction.

After the fusion promoting material is introduced into the base member,the closure member can be engaged and locked to the base memberaccording to an aspect of the present invention. In general, however,this manner of constructing the implant in situ within the interbodyspace offers a host of additional features beyond those of traditionalinterbody implants of unibody construction. It offers an enhanced safetyprofile based on the protection offered by the base member during finalendplate preparation, which forms a barrier such that the associatedinstruments for final endplate preparation cannot be inadvertentlypassed or extended outside the disc space by the surgeon and intocontact with the adjacent neural and vascular structures. It offersincreased efficiency in final endplate preparation by limiting the areaof final endplate preparation to just that area within the interior ofthe base member. It also advantageously separates the weight bearingportion of the base member (i.e. the upper and lower contact surfaces)from the potential fusion area created within the interior of the basemember, thereby allowing for an aggressive removal of the cartilaginousendplates within interior of the base member (e.g. extending into thecancellous bone to cause ample bleeding to promote the fusion process).

In situ formation of the implant of the present invention also preventsor reduces the risk of subsidence of the implant into the softercancellous bone in two distinct manners. First, it does so by notrequiring the cartilaginous endplates to be removed prior to implantintroduction as is required with traditional implants. In other words,this allows the cartilaginous endplates to provide protection againstfracturing the underlying vertebral body during the introduction of thebase member, which can occur during the implantation of traditionalinterbody implants of unibody construction if the surgeon is not carefulto avoid. It also prevents or reduces subsidence by allowing the lengthof the closure member to be selected after the implantation of the basemember to maximize the surface area of the overall implant to ensureleading and trailing ends of the result implant are positioned on thestronger cortical bone forming the ring apophysis around the peripheryof the vertebral bodies. In this regard, both the base member and theclosure member are in direct contact with upper and lower vertebralbodies, thereby bearing weight and sharing the associated loads. Theheight of the closure member can also be determined after theimplantation of the base member and may be different from the height ofthe base member, allowing for possible correction of a coronal deformityin the interbody space.

Finally, in situ implant formation also advantageously allows a surgeonto aggressively pack the fusion promoting material into the implant morethan may be capable with conventional implants of unibody construction.This is because the surgeon need only pack the fusion promoting materialinto the base member after implantation, as opposed to impacting animplant that has been packed with fusion promoting material beforeimplantation and dislodge or loosen the fusion promoting material as isthe case with traditional implants.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective exploded view of an interbody fusion implantincluding a base member and a closure member according to an aspect ofthe present invention;

FIG. 2 is a cross sectional view of a patient during lateral accesssurgery with the base member of FIG. 1 in the interbody space (withfinal endplate preparation having been performed after the implantationof the base member) according to aspects of the present invention;

FIG. 3 is a cross sectional view of a patient during lateral accesssurgery with the closure member of FIG. 1 attached to the base member ofFIG. 1 (with fusion promoting material disposed therein, having beenintroduced after the implantation of the base member but before theimplantation of the closure member) according to aspects of the presentinvention;

FIG. 4 is a top exploded view of the interbody fusion implant of FIG. 1according to an aspect of the present invention;

FIG. 5 is a top exploded view, in partial cross section, of theinterbody fusion implant of FIG. 1 illustrating the locking featuresbetween the base and closure members before engagement and locking ofthe closure member to the base member according to an aspect of thepresent invention;

FIG. 6 is a top view, in partial cross section, of the interbody fusionimplant of FIG. 1 illustrating the locking features between the base andclosure members after engagement and locking according to an aspect ofthe present invention;

FIG. 7 is a perspective view of an inserter for use with the base memberof the interbody fusion implant of FIG. 1 according to an aspect of thepresent invention;

FIGS. 8 and 9 are perspective views of the inserter of FIG. 7 and thebase member of FIG. 1 before and after, respectively, coupling togetheraccording to an aspect of the present invention;

FIG. 10 is a perspective view of an inserter for use with the closuremember of the interbody fusion implant of FIG. 1 according to an aspectof the present invention;

FIG. 11 is a perspective enlarged view of the distal end of the inserterof FIG. 10 according to an aspect of the present invention;

FIGS. 12 and 13 are perspective views of the inserter of FIG. 10 and theclosure member of FIG. 1 before and after, respectively, couplingtogether according to an aspect of the present invention;

FIG. 14 is a top view of a patient in the lateral decubitus position inpreparation for lateral access surgery;

FIG. 15 is a posterior view of a patient in the lateral decubitusposition in preparation for lateral access surgery illustrating aspectsand general positioning of the lumbar and thoracic spine;

FIG. 16 is a side view of a prior art retractor system positionedlaterally relative to the patient's lumbar spine in preparation for theimplantation of the interbody fusion implant of FIG. 1 according to anaspect of the present invention;

FIG. 17 is a lateral view down an operative corridor established by theprior art retractor system of FIG. 16 before an annulotomy anddiscectomy are performed in preparation for the implantation of theinterbody fusion implant of FIG. 1 according to an aspect of the presentinvention;

FIG. 18 is a cross sectional view of a patient during lateral accesssurgery after an annulotomy and preliminary discectomy have beenperformed in preparation for the implantation of the interbody fusionimplant of FIG. 1 according to an aspect of the present invention;

FIG. 19 is a cross sectional view of a patient during lateral accesssurgery illustrating the optional step of sizing/distracting the discspace before introducing the base member of FIG. 1 according to anaspect of the present invention;

FIG. 20 is a cross sectional view of a patient during lateral accesssurgery illustrating the step of introducing the base member of FIG. 1with the associated inserter of FIG. 7 according to an aspect of thepresent invention;

FIG. 21( a) is a cross sectional view of a patient during lateral accesssurgery illustrating the step of final end plate preparation after theintroduction of the base member of FIG. 1, but before the introductionof the closure member of FIG. 1, according to an aspect of the presentinvention;

FIG. 21( b) is an enlarged view of the trailing end of the base memberafter final endplate preparation according to an aspect of the presentinvention;

FIG. 22 is a cross sectional view of a patient during lateral accesssurgery illustrating the step of introducing fusion promoting materialinto the finally prepared disc space within the base member of FIG. 1according to an aspect of the present invention;

FIG. 23 is a cross sectional view of a patient during lateral accesssurgery illustrating the step of introducing the closure member of FIG.1 for the engagement with the base member of FIG. 1 according to anaspect of the present invention;

FIG. 24 is a flow chart describing the method steps involved inimplanting an interbody fusion implant according to an aspect of thepresent invention;

FIG. 25 is a perspective exploded view of an interbody fusion implantincluding a base member and closure member according to another aspectof the present invention;

FIG. 26 is a top exploded view of the base member and closure member ofFIG. 24 before engagement and locking together according to an aspect ofthe present invention;

FIG. 27 is a top view of the base member and closure member of FIG. 24after engagement and during the process of locking together according toan aspect of the present invention;

FIG. 28 is a side view of interbody fusion implant of FIG. 24 afterlocking the closure member to the base member according to an aspect ofthe present invention;

FIG. 29 is an end view of the closure member of FIG. 24 illustrating theengagement features for coupling the closure member to an inserter aswell as the locking screw element for locking the closure member to thebase member according to an aspect of the present invention;

FIG. 30 is a perspective exploded view of an interbody fusion implantincluding a base member and a closure member according to yet anotheraspect of the present invention;

FIG. 31 is a top exploded view of the interbody fusion implant of FIG.30 according to an aspect of the present invention;

FIG. 32 is a perspective view of the closure member of FIG. 30 accordingto an aspect of the present invention;

FIG. 33 is a perspective exploded view of an interbody fusion implantincluding a base member and a closure member according to a stillfurther aspect of the present invention;

FIGS. 34 and 35 are top and end views, respectively, of the base memberof FIG. 33 illustrating slot features for coupling the closure member tothe base member according to an aspect of the present invention;

FIG. 36 is a side view of one arm of the base member of FIG. 33 furtherillustrating the slot features for engaging the closure member to thebase member, as well as a recess for receiving locking prongs of theclosure member of FIG. 33 according to an aspect of the presentinvention;

FIG. 37 is a perspective view of the closure member of FIG. 33 accordingto an aspect of the present invention; and

FIGS. 38 and 39 are perspective views of an inserter for use with thebase member of FIGS. 25-29 before and after, respectively, couplingtogether according to an aspect of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Illustrative embodiments of the invention are described below. In theinterest of clarity, not all features of an actual implementation aredescribed in this specification. It will of course be appreciated thatin the development of any such actual embodiment, numerousimplementation-specific decisions must be made to achieve thedeveloper's specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming, but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure. The interbody implant, inserters, and associatedmethodology for spinal fusion using a lateral approach to the spinedisclosed herein boasts a variety of inventive features and componentsthat warrant patent protection, both individually and in combination.

FIG. 1 is a perspective exploded view of an interbody fusion implant 10including a base member 12 and a closure member 14 according to anaspect of the present invention. The base member 12 and closure member14 are complimentary to each other so that they can be engaged andthereafter locked together while in a lumbar or thoracic intervertebral(aka interbody) space. The base member 12 is configured in a generallyelongated U-shaped manner with generally parallel side walls 16 coupledto an end wall 18 positioned generally perpendicularly with the sidewalls 16. The base member 12 includes, by way of example only, lockingfeatures in the form of locking pins 20 extending longitudinally awayfrom the trailing ends of the side walls 16. The closure member 14includes a main body 22 with complimentary locking features in the formof recesses 24 to receive the locking pins 20 of the base member 12 andextensions 26 extending generally longitudinally away from the main body22 towards the base member 12. The mechanics and operation of thisexemplary locking mechanism will be described in greater detail below.

With reference to FIGS. 2 and 3, according to an aspect of the presentinvention, the base member 12 is introduced into the interbody spacebefore the closure member 14. By doing so, and given the U-shapedconfiguration of the base member 12, this allows for inspection of thebase member 12 to ensure optimal positioning before final endplatepreparation, an aggressive final vertebral end plate preparation tocreate a fully prepared fusion area 13 with the base member 12, andpacking of fusion promoting material 15 into the fusion area 13 afterthe base member 12 has been implanted but before the closure member 14is implanted (FIG. 2). This presents a host of benefits, which will bedescribed in detail below, along with the specific method stepsassociated with the use of the base member 12 and closure member 14during lateral access surgery according to an aspect of the presentinvention. The introduction of the base member 12 is facilitated throughthe use of a specialized inserter (not shown, but described below)designed to bolster the structural integrity of the base member 12during insertion to reduce the likelihood of having the base member 12fracture under the impaction forces typically involved in interbodyfusion cases. The introduction of the base member 12 is also facilitatedvia the slightly tapered leading end 28, which serves as a general wedgebetween the adjacent vertebral bodies during insertion of the basemember 12 into the disc space during impaction.

After the fusion promoting material is introduced into the base member12, the closure member 14 can be engaged and locked to the base member12 as shown generally in FIG. 3 and as will be described in greaterdetail below. In general, however, this manner of constructing implant10 in situ within the interbody space is advantageous in that it allowsa surgeon to aggressively and efficiently prepare the bony endplatesthat will serve for a fusion bed within the base member 12 while thesides of the base member 16, and 18 protect the surroundingneurovascular structures (such as the vena cava VC, aorta A andposterior neural structures NS) as well as the weight bearing portionsof the vertebral end plates. The design also allows the surgeon toaggressively pack fusion promoting material into the implant 10 morethan may be capable with conventional, unitary designs. In addition, thelength of the closure member 14 may be selected after the implantationof the based member 12 to maximize the surface area of the over implant10 to ensure the leading and trailing ends of the implant 10 arepositioned on the stronger cortical ring apophysis of the vertebralbodies, thereby minimizing the risk of subsidence into the softercancellous region. In this regard, both the base member 12 and theclosure member 14 are in direct contact with upper and lower vertebralend plates, thereby bearing weight and sharing the loads from the endplates. The height of the closure member 14 can also be determined afterthe implantation of the base member 12 (differing from the height and/orcurvature of the base member 12) allowing for possible of correction ofcoronal deformity within the disc space or adjacent vertebral bodies.

With reference to FIGS. 4-5, by way of example only, according to anaspect of the present invention the base member 12 includes locking pins20 and the closure member 14 includes recesses 24. The closure member 14has two tabs 26 extending outward in the opposite direction of therecesses 24. The tabs 26 align the closure member 14 with the basemember 12 when the closure member 14 is being attached to the basemember 12 in the interbody space. Both the base member 12 and theclosure member 14 include a series of anti-migration features 32 on theupper and lower surfaces 34, 36 to help prevent migration of the implantrelative to the adjacent vertebral bodies while in the interbody space.Although shown as angled teeth, the anti-migration features 32 may beconfigured and arranged in any number of suitable manners and structuressufficient to prevent or minimize the propensity for the implant 10 tomigrate or move after implantation.

As shown in FIG. 5, the locking pins 20 of the base member 12 are (byway of example only) separate components that are affixed to the basemember 12 prior to the installation of the base member 12 into theinterbody space. By using separate pieces for the locking pins 20, thelocking pins 20 can be of the same or different material than that ofthe base member 12. In one aspect, the locking pins 20 may be of ametallic construction to simultaneously serve as radiopaque markers toaid in the visualization of the base member 12 or implant 10 duringand/or after implantation, particularly when the base member 12 andclosure member 14 are constructed of radiolucent material, such aspoly-ether-ether-ketone (PEEK) and/or other suitable biocompatible andradiolucent materials. Although shown as separate components in FIG. 5,the base member 12 and locking pins 20 may be constructed in a unitaryfashion without departing from the scope of the invention. Similarly,the locking features shown and described with reference to FIG. 5 couldbe reversed, with the locking pins 20 extending from the closure member14 and the tabs 26 extending from the base member 12, without departingfrom the scope of the invention.

In either event, the recesses 24 of the closure member 14 are preferablycomplimentary to the shape of the locking pins 20 of the base member 12to facilitate the engagement of the closure member 14 to the base member12 during use. Depending upon the tolerance between the recesses 24 andthe locking pins 20, the sheer act of advancing the locking pins 20within the recesses 24 may serve as the primary (and possibly only)manner of locking the closure member 14 to the base member 12 via aresulting friction fit. To facilitate this, locking pins 20 may includea variety of serrations 38 to help engage the interior of the recesses24. If desired, the recesses 24 and locking pins 20 may be dimensionedto allow for some clearance between the serrations 38 of the lockingpins 20 and the interior of the recesses 24.

As best shown in FIGS. 5-6, a secondary locking mechanism may also beprovided according to an aspect of the present invention, such as (byway of example only) equipping the closure member 14 with an actuatingelement 40 and a pair of transverse pins 42. The actuating element 40 isdisposed within a longitudinal recess 44 extending (by way of exampleonly) along the longitudinal axis of the implant 10. The transverse pins42 are disposed within corresponding transverse apertures 46 extending(by way of example only) generally perpendicularly from the longitudinalrecess 44. As best shown in FIG. 5, prior to actuation (i.e. axialtranslation towards the interior of the implant 10), a trailing end 48of the actuation element 40 extends slightly past the longitudinalrecess 44 and a beveled leading end 50 is barely (if at all) in contactwith the medial ends 48 of the transverse pins 42.

As best shown in FIG. 6, upon actuation, the trailing end 48 is movedaxially within the longitudinal recess 44 such that the beveled leadingend 50 forces the transverse pins 42 into axial translation within thetransverse apertures 46 and into physical engagement with the lockingpins 20 of the base member 12 which are disposed within the recesses 24of the closure member 14. This action serves to form a secondary lockbetween the closure member 14 and the base member 12. The actuationelement 40 may be any number of different mechanisms for driving thetransverse pins 42 into the locked position against the locking pins 20,including but not limited to a set screw type component as shown inFIGS. 5-6. The serrations 38 of the locking pins 20 advantageously aidin establishing purchase with the pointed end of the transverse pins 42to thereby augment the locking ability between the closure member 14 andbase member 12. The serrations 38 may also be angled as shown in FIG. 6in order to make them easier to insert within the recesses 24 than toremove from the recesses 24. The transverse pins 42 may be of a metallicconstruction to simultaneously serve as radiopaque markers to aid in thevisualization of the closure member 14 or the implant 10 during and/orafter implantation, particularly when the base member 12 and closuremember 14 are constructed of radiolucent material, such aspolyether-ether-ketone (PEEK) and/or other suitable biocompatible andradiolucent materials.

The actuation element 40 as described above provides a number ofbenefits, including allowing a final inspection of the base member 12and closure member 14 before the actuation element 40 is advanced to thelocking position shown in FIG. 6. As such, if the sizing or the positionof the implant 10 is determined to be less than optimal or for whateverreason undesirable by the surgeon, they have the option of simplyremoving the closure member 14 without first needing to back out theactuation element 40 and disengage the transverse pins 42 from thelocking pins 20. Another benefit is that, by positioning the actuationelement 40 within the longitudinal aperture 44 of the closure member 14during the introduction of the closure member, it prevents any bodilytissues from building up or becoming lodged in the longitudinal aperture44. A still further benefit is that, once the fully assembled implant 10is packed with fusion promoting material 52 (as illustrated in FIG. 3),the fusion promoting material does not have an aperture to allow for anegress route through the closure member 14.

According to an aspect of the present invention, the base members 12 andclosure members 14 shown herein may be introduced into an interbodyspace via any number of suitable insertion instruments. By way ofexample only, FIGS. 7-9 illustrate an inserter 60 for use in introducingthe base member 12 of FIGS. 1-6 into an interbody space according to anaspect of the present invention. As best viewed in FIG. 7, the inserter60 includes an elongated shaft 62 with a handle region 64 and aninsertion region 66 disposed at either end. The elongated shaft 62 ishollow in construction and houses a coaxially aligned inner shaft havinga threaded distal end 68 and a proximal end coupled to a thumb wheel 70located in the handle region 64. The insertion region 66 includes a mainbody 72 and lateral members 74 extending generally laterally from thetrailing end at the approximate junction with the elongated shaft 62.The main body 72 has a peripheral shape that is generally complimentaryto the interior shape of the base member 12 as defined by the side walls16 and end wall 18. The lateral members 74 are dimensioned to abut thetrailing ends 76 of the side walls 16 when the main body 72 ispositioned within the base member 12. The lateral members 74 have eachhave a recess 30 extending generally longitudinally within the lateralmembers 74 dimensioned to accommodate and receive the locking pins 20 ofthe base member 12 to facilitate engagement between the base member 12and inserter 60. The threaded distal end 68 extends beyond the leadingend 78 of the main body 72.

As best viewed in FIGS. 8-9, by rotating the thumb wheel 70, thethreaded distal end 68 can be selectively engaged and disengaged withthe corresponding threaded aperture 80 formed in the end wall 18 of thebase member 12. More specifically, advancing the thread 68 into to basemember 12 causes the base member 12 to be pulled towards the main body72 of the inserter 60 until the inner surface 82 of the base member 12is fully mated with the peripheral surface 84 of the inserter 60 asshown in FIG. 9. The advancement of the base member 12 toward the mainbody 72 of the inserter also results in the advancement of the lockingpin 20 in the recesses 30 of the lateral member 74, thereby providingrotational stability during insertion into the patient. Once fullyseated in this manner, the base member 12 is ready to be inserted intothe interbody space according to an aspect of the present invention.After implantation, as will be described in greater detail below, theinserter 60 can be selectively disengaged from the base member 12 byreversing the direction the thumb wheel 70 and thus disengaging thethreaded distal end 68 from the corresponding recess 80. This movementwill also withdraw the locking pin 20 form the recesses 30 of thelateral members 74.

According to an aspect of the present invention, the complimentary shapeof the insertion region 66 relative to the base member 12 bolsters thestructural integrity of the base member 12 during the process ofimplantation. More specifically, the elongated and open nature of thegenerally U-shaped base member 12 causes it to be relatively weak interms of resisting sheer forces that may otherwise occur if the basemember 12 were introduced by applying forces to one or both of thetrailing ends 76 of the side walls 16 or only the end wall 18. Instead,the insertion region 66 is dimensioned to maximize the surface areabetween the main body 72 and the interior of the base member 12.

FIGS. 10-13 illustrate an inserter 90 for the closure member 14 of FIGS.1-6 according to an aspect of the present invention. As shown in FIGS.10-11, the inserter 90 includes an elongated shaft 92 with a handleregion 94 and an insertion region 96 disposed at either end. Theelongated shaft 92 is hollow in construction and houses a coaxiallyaligned inner shaft 98 having a proximal end coupled to a knurled member100 of the handle region 94 and a pair of distal ends 102 separated by agap 104 extending a predetermined distance within the distal end 106 ofthe hollow elongated shaft 92. The inner shaft 98 also includes a pairof arm members 108, with each arm member 108 having a prong member 110extending longitudinally away from a distal surface 112. The inner shaft98 is also generally hollow in construction and houses a driver member114 (by way of example only, a hex driver) having a proximal endextending beyond the handle region 94 and a distal end extending beyondthe arm members 108 of the inner shaft 98.

In addition to the knurled element 100, the handle region 94 alsoincludes a counter-torque element 116 coupled to the proximal end 118 ofthe elongated shaft 92. The counter-torque element 116 allows thesurgeon to hold the elongated shaft 92 relatively stationary as theknurled member 100 is rotated relative to the elongated shaft 92 or viceversa. Although not shown, the interior of the proximal end 118 of theelongated shaft 92 has a threaded configuration which cooperates with athreaded configuration located on the inner shaft 98 adjacent to theknurled member 100. By rotating the inner shaft 98 relative to theelongated outer shaft 92, the insertion region 96 will be translatedaxially towards the distal end of the elongated shaft 92. This, in turn,will cause the arm members 108 to be moved towards one another, therebyreducing the gap 104.

As best viewed in FIGS. 12-13, to couple the inserter 90 to the closuremember 14, the inserter 90 is advanced such that the prong members 110on the arm members 108 extend into the recesses 24 for the locking pins20 (see FIG. 5). At that point, with the closure member 14 in abutmentwith the distal surface 112 of the arm members 108, the knurled member100 may be rotated relative to the counter-torque element 116 (or viceversa) such that the arm members 108 are forced towards one another andthereby exert a compression force between the prong members 110 whichacts upon the closure member 14 via the recesses 24 to temporarily lockthe closure member 14 to the inserter 90. Once fully seated in thismanner, the closure member 14 is ready to be inserted into the interbodyspace according to an aspect of the present invention, namely, to engageand then lock with the base member 12. After implantation, as will bedescribed in greater detail below, the inserter 90 can be selectivelydisengaged from the closure member 14 by reversing the direction theknurled member 100 relative to the anti-torque element 116 and thusdisengaging the prongs 110 from the corresponding recesses 24. Beforedoing so, however, the driver member 114 may be optionally employed todrive the actuation element 40 of the closure member 14 as describedabove in order to selectively deploy the transverse pins 42 with thegoal of providing a secondary locking between the closure member 14 andthe base member 12. The driver 114 is shown, by way of example only,with a hexagonal shape rod 120 dimensioned to engage with the proximalend of the actuation element 40 to engage and/or disengage the lockingmechanism.

The inserter 90 thus provides the dual advantages of providing both amechanism to affix the inserter 90 to the closure member 14 as well asthe ability to engage and operate the actuation element 40 to lock theclosure member 14 to the base member 12. That said, it will beappreciated that the inserter 90 can be used for the purpose ofinserting the closure member 14 into the disc space without having theability to lock the closure member 14 to the base member 12, such aswhere the secondary locking features (e.g. transverse pins 42 andactuation element 40) are not required. Although shown and described inthis specific manner, it will be appreciated that the closure member 14may be coupled to the inserter 90 in any number of suitable manners,including but not limited to the same or similar mechanism as used inFIG. 9, namely, a threaded rod that threads into a correspondingthreaded hole. It is also contemplated to construct the closure member14 to include two different sized threaded holes, one for the actuationelement 40 and one for an additional threaded rod 68 as described above.

The methodology associated with using the implant 10 during lateralaccess surgery according to an aspect of the present invention will nowbe described with reference to FIGS. 14-23, as well as the flow chart inFIG. 24. The first step involves gaining lateral access to the patient'slumbar or thoracic spine (step 130 in FIG. 24). This is performed byfirst (FIGS. 14-15) positioning the patient in the lateral decubitusposition and then (FIGS. 16-17) establishing a lateral operativecorridor 122 via the introduction of an access system such as the priorart retractor 124 shown by way of example only. With the operativecorridor 122 established, an annulotomy and preliminary discectomy(steps 132, 134 in FIG. 24) must then be performed with the goal ofcreating an implant region 17 as shown in FIG. 18 capable of receiving afully assembled implant 10 according to an aspect of the presentinvention. The implant region 17 preferably extends from the ipsilateralcortical bone region 19 to the contralateral cortical bone region 21 andthe intervening cancellous bone region 23 of the underlying vertebralbody. (Although shown fully removed on the contralateral bone region 21in the interest of clarity, the annulus in that area may simply be“released” (cut but not fully removed) in order to accommodate at leasta portion of the leading end of the base member 12.)

The next step (136 in FIG. 24) involves the process of sizing the basemember 12 to ensure the desired restoration of disc height, sagittal andcoronal balance, etc . . . This can be facilitated by (FIG. 19) using asizer/distractor instrument 128 for the purpose of identifying theproper amount of disc height restoration as well as loosening up thejoint to facilitate the introduction of the base member 12. Dependingupon the pathology and anatomy, the base member 12 may be selectedhaving any of a variety of suitable heights, lengths, widths, lordotictapers, coronal tapers, etc . . . Based on the ability to select anoptimally sized closure member 14 after the fusion promoting materialhas been packed into the base member 12, it may be possible to have basemembers 12 of relatively standard or uniform length (albeit with varyingheight, width and curvature dimensions) in order to minimize theinventory required for surgery, as well as reduce the amount of timerequired for selecting a base member 12. The key is that the leading endof the base member 12 be positioned at least partially on thecontralateral cortical region 21, as will be discussed in greater detailbelow.

Once the desired size of the base member 12 is determined (optimal orstandard), the base member 12 may be inserted into the interbody space(step 138 in FIG. 24). This is accomplished by coupling the base member12 to the inserter 60 and impacting it into the implant region 17 asshown in FIG. 20 via the use of any number of well known impaction tools(not shown). The base member 12 should be preferably located within thedisc space (more specifically, within the implant region 17 shown inFIGS. 18-19) such that the leading end (end wall 18) is positioned atleast partially on the contralateral cortical bone region 21 as shown inFIG. 20. With the base member 12 positioned in this manner, the inserter60 may then be disconnected and the inserter 60 removed such that thebase member 12 is the only element disposed in the disc space.

FIGS. 21( a) illustrates the next step (140 in FIG. 24) of finalendplate preparation, which may be accomplished via any number of wellknown endplate preparation tools, including but not limited to scraper129 shown in FIG. 21( a), to create the fusion region 13 within theinterior of the base member 12 and extending to the ipsilateral corticalbone region 19. In the interest of added clarity, FIG. 21( b)illustrates the trailing end of the base member 12 (and the surroundingarea) after final endplate preparation to further detail the relation ofthe resulting fusion region 13 to the previously prepared implant region17. According to an aspect of the present invention, the fusion area 13is an exact, reproducible region separated from the neurovascularstructures (aorta A, vena cava VC and posterior neural structures NS) byvirtue of the side walls 16 and end wall 18 of the base member 12,thereby providing an added level of safety against the inadvertentpositioning of the endplate preparation instruments past or outside thedisc space during endplate preparation. Due to the protective feature ofthe base member 12, as well as the fact the upper and lower surfaces ofthe base member 12 rest upon the cartilaginous endplate exposed afterthe preliminary discectomy, the surgeon may be more aggressive inremoving the cartilaginous endplates, intentionally scraping into theunderlying cancellous bone to ensure sufficient bleeding for the fusionprocess to occur in a robust and timely manner.

With the base member 12 in position and the endplates fully prepared forfusion, the surgeon may (step 142 in FIG. 24) introduce and optionallypack any of a variety of fusion promoting materials within the basemember 12 via (by way of example only) a packing funnel 131 such asshown generally in FIG. 22. Fusion promoting materials may include, butare not necessarily limited to, cancellous autograft bone, allograftbone, demineralized bone matrix (DBM), porous synthetic bone graftsubstitute, bone morphogenic protein (BMP), mesenchymal stem cellsand/or combinations thereof and/or functional equivalents. Introducingthis material after the base member 12 has been implanted isadvantageous in that it increases the likelihood that the density of thefusion promoting material will be greater than if loaded and packedbefore introduction into the interbody space. This is because, withtraditional implants which are packed prior to implantation, theimpaction process tends to dislodge or loosen the fusion promotingsubstance. By packing the base member 12 after implantation, the surgeoncan pack this material as densely as they can/wish before enclosing thecavity with the closure member 14 during lateral access surgeryaccording to an aspect of the present invention.

Before enclosing the base member 12, the closure member 14 shouldpreferably be sized (step 144 in FIG. 24) to ensure the optimal length,height, taper, etc . . . for the desired amount of disc heightrestoration as well as (optionally) the preferred degree of sagittaland/or coronal re-alignment of the adjacent vertebral bodies. This canbe facilitated by any number of suitable sizing tools (not shown), aswell as via radiographic methods (e.g. MRI, X-ray, fluoroscope, etc . .. ) and even any of a variety of depth gauges (not shown). The end goalis determine the optimal size to ensure that the resulting implant 10,after being formed in situ in the disc space, is positioned such that atleast a portion of the leading end (end wall 18 of base member 12) andat least a portion of the trailing end (body 22 of the closure member14) are positioned on the contralateral cortical bone region 21 andipsilateral cortical bone region 19, respectively, as shown in FIG. 3and partially in FIG. 23. This minimizes the risk of subsidence into thesofter cancellous region. In this regard, both the base member 12 andthe closure member 14 are in direct contact with upper and lowervertebral end plates, thereby bearing weight and sharing the loads fromthe end plates. Depending upon the pathology and anatomy, the closuremember 14 may be selected having any of a variety of suitable heights,lengths, widths, lordotic tapers, coronal tapers, etc . . . includingthose different from the base member 12 in order to (by way of exampleonly) tailor the degree of lordosis (in the lumbar spine), kyphosis (inthe thoracic spine) and/or coronal realignment (in the lumbar orthoracic spine) after the base member 12 has been implanted.

Once the optimal size of the closure member 14 has been determined, theclosure member 14 may be inserted into the interbody space (step 146 inFIG. 24). This is accomplished by coupling the closure member 14 to theinserter 90 as shown and described above with reference to FIGS. 12-13and then impacting it into the interbody space 126 and locking it to thebase member 12 as shown and described with reference to FIGS. 5-6. FIG.3 illustrates the end result, with the implant 10 formed in situ withthe interbody space extending laterally with at least a portion of theleading end (end wall 18 of base member 12) resting on the contralateralcortical bone region 21 and at least a portion of the trailing end (body22 of the closure member 14) resting on the ipsilateral cortical boneregion 19. With the implant 10 filled with fusion promoting material 15and enclosed via the combination of the closure member 14 and the basemember 12, the retractor 124 may be removed and the wound closed (step148 in FIG. 24) as is well known in the art.

Having described in detail the specifics of one type of implant 10according to an aspect of the present invention, as well as theassociated insertion instruments 60, 90 and methodology in lateralaccess surgery, a variety of additional implants forming aspects of thepresent invention will now be described. Based on many of the commonfeatures and/or functionality with the implant 10 described above, thefollowing description and the associated drawings will not includespecific references to associated inserters or much (if any) addeddetail regarding the associated methodology, as such is deemedduplicative and unnecessary.

FIGS. 25-29 illustrate an interbody fusion implant 150 including a basemember 12 and closure member 14 according to another aspect of thepresent invention. The implant 150 is virtually identical to the implant10 of FIGS. 1-23 except that the closure member 14 and base member 12have a different locking mechanism. In particular, the closure member 14includes a pair of bendable hook elements 152 extending towards the basemember 12, and the side walls 16 of the base member 12 each include arecess 154 to receive the hook elements 152 after they have been forcedinto lateral movement by the axial advancement of the actuator element40 of the closure member 14. The trailing end of the closure member 14may be configured with any suitable engagement features for coupling toa suitable inserter, such as the slotted arrangement shown in FIG. 29with the actuation element 40 disposed in the approximate midline. Allother features in common with the implant 10 of FIGS. 1-23 are denotedwith the same reference numbers and an explanation of then functionalitymay be ascertained with reference to the discussion of those similarfeatures with reference to FIGS. 1-23.

FIGS. 30-32 illustrate an interbody fusion implant 160 including a basemember 12 and a closure member 14 according to yet another aspect of thepresent invention. The base member 12 has a rigid, elongated structurerectangular in nature. The base member 12 includes a supplemental wall162 near the end wall 18 that defines a proximal opening 164 and adistal opening 166. The distal opening 166 may receive fusion promotingmaterials before the introduction of the base member 12, while theproximal opening 164 is dimensioned to receive fusion promotingmaterials after implantation of the base member 12 but before enclosureby the closure member 14. The closure member 14 includes two lockingpins 168 extending longitudinally towards the base member 12, and thebase member 12 includes two corresponding recesses 169 to receive thelocking pins 168 for purposes of locking the closure member 14 to thebase member 12. As best viewed in FIG. 32, the locking pins 168 have agenerally “mushroom” shape with angled elements 167 that bend in orderto permit the locking pin 168 to easily pass through the recesses 169and then rebound and flare out to prevent the disengagement of theclosure member 14 from the base member 12.

FIGS. 33-37 illustrate an interbody fusion implant 170 including a basemember 12 and a closure member 14 according to a still further aspect ofthe present invention. The base member 12 has a generally U-shape withelongated slots 172 extending along the interior of the side walls 16from the proximal end 76 to a point a predetermined distance towards theend wall 18. The side walls 16 also each include a recess 174 extendingthrough the side wall 16 to intersect with the elongated slots 172. Theclosure member 14 includes a pair of elongated hooks 176 extendingtowards the base member 12. The elongated hooks 176 are generallycompliant and bendable such that they will engage within the elongatedslots 172 and deform slightly towards one another upon the applicationof axial force against the closure member 14 towards the base member 12.The distal region 178 of the hooks will pass along the slots 172 untilthey reach the recesses 174, at which point they will automaticallyrebound and move away from one another to force the distal regions 178into the recesses 174 to lock the closure member 14 to the base member12.

The closure member 14 also includes a wedge element 177 extendingtowards the base member 177 according to an aspect of the presentinvention. The wedge shape 177 allows for ease of insertion of theclosure member 14 into the interbody space once the base member 12 hasalready been installed. The wedge shape 177 is an additional shape tothe closure member 14, and once installed together with the base member12, both the top and bottom surfaces 34, 36 are to be in direct contactwith the end plates. The contacting surfaces 34, 36 allow the implant,both the closure member 14 and the base member 12, to the support weightand to share the loads from the endplates.

According to an aspect of the present invention, the implants describedherein can be adapted for different applications and patient pathologiesby selectively varying the heights, widths, lengths, lordotic taper andcoronal taper in any suitable increment (e.g. 1-2 mm increments for L,W,H and 1-2 degrees for tapers). By way of example only, the implants ofthe present invention may be provided in lengths ranging from 35-65 mm,heights ranging from 6-18 mm, width ranging from 18-30 mm, lordotictapers ranging from 0-12 degrees, and coronal tapers ranging from 0-15degrees. The individual base members and closure member may also besized in any number of suitable manners, including: (a) for basemembers, lengths ranging from 30-50 mm, heights ranging from 6-18 mm,widths ranging from 18-30 mm, lordotic tapers ranging from 0-12 degrees,and coronal tapers ranging from 0-15 degrees, and (b) for the closuremembers, lengths ranging from 5-25 mm, heights ranging from 6-18 mm,widths ranging from 18-30 mm, lordotic tapers ranging from 0-12 degrees,and coronal tapers ranging from 0-15 degrees.

As noted above, any number of inserters can be used to implant the basemembers 12 and closure members 14 disclosed herein according to anaspect of the present invention, including those designs illustrated inFIGS. 25-37. This is evidenced, by way of example only, with referenceto FIGS. 41-42, which show the distal end of an inserter 200 for usewith the base member 12 of FIGS. 25-29. The inserter 200 is of the samegeneral construction and configuration as the inserter 60 of FIGS. 7-9,except that the lateral members 74 of the insertion region 66 aredimensioned in a generally acutely angled manner to abut the generallyangled trailing ends 76 of the side walls 16 when the main body 72 ispositioned within the base member 12. In this manner, the insertionregion 66 retains the trailing ends 76 of the side walls 16 by causingthe trailing ends 76 to be disposed within the acute angle formed by thelateral members 74, thereby preventing any unwanted splay duringintroduction. Other than this distinction, the inserter 200 operates inthe same manner as the inserter 60 such that the description need not berepeated.

Having described a multitude of aspects of the present invention,including aspects of the interbody fusion implant, the inserters foreach member of the interbody fusion implant, and associated methodology,it should be understood that this invention is not limited to only thoseaspects described above and that changes and modifications may be madewithout departing from the true spirit and scope of the invention asdefined in the appended claims.

What is claimed is:
 1. A method of performing lateral interbody fusionof an affected intervertebral disc within a patient's lumbar or thoracicspine, the disc including nucleus pulposus surrounded by an annulus, andthe disc bounded by adjacent vertebral bodies, each having an innercancellous bone region bounded by an outer cortical bone region,comprising the steps of: (a) creating an operative corridor to anaffected disc in the lumbar or thoracic spine by using a lateralapproach to the spine; (b) creating an implant region within theaffected disc extending from an ipsilateral aspect of the cortical boneregion to a contralateral aspect of the cortical bone region, andincluding the cancellous bone region extending there between; (c)implanting a base member having a side walls and an end wall such thatat least a portion of the end wall provides structural support betweencontralateral aspects of the cortical bone regions of the adjacentvertebral bodies, the side walls and end wall of the base memberdefining an open trailing end and an interior bounded by the side wallsand end walls, the side walls and end wall forming a protective barrierbetween the interior of the base member and surrounding neural tissuesand/or vasculature; (d) performing final endplate preparation within theinterior of the base member to define a fusion area within thecancellous bone adjacent to the interior of the base member; (e)introducing fusion promoting material into the interior of the basemember and into contact with the fusion area of the exposed cancellousbone; (f) implanting a closure member such that it encloses the interiorof the base member after the fusion promoting material has beenintroduced and such that at least a portion of the closure memberprovides structural support between ipsilateral aspects of the corticalbone regions of the adjacent vertebral bodies; and (g) closing theoperative corridor.
 2. The method of performing lateral interbody fusionof claim 1, wherein step (b) involves performing an annulotomy on anipsilateral aspect of the annulus, a partial discectomy of the nucleuspulposus, and at least a partial release of the contralateral annulus tocreate the implant region within the affected disc.
 3. The method ofperforming lateral interbody fusion of claim 1, wherein step (c)involves selecting the base member in order to achieve a desiredrestoration of disc height, sagittal balance and/or coronal balance. 4.The method of performing lateral interbody fusion of claim 3, whereinselecting the base member includes at least one of the steps of sizingand distracting.
 5. The method of performing lateral interbody fusion ofclaim 1, wherein step (f) involves selecting the closure member in orderto achieve a desired restoration of disc height, sagittal balance and/orcoronal balance.
 6. The method of performing lateral interbody fusion ofclaim 5, wherein selecting the closure member involves determining theoptimal size and shape of the closure member to ensure at least aportion of the closure member provides structural support between theipsilateral aspects of the cortical bone regions of the adjacentvertebral bodies.
 7. The method of performing lateral interbody fusionof claim 6, wherein the closure member may be selected having differentheight or shape dimensions as the base member in order to customize thedegree of sagittal and/or coronal balance of the patient's spine.